Paracrine Release of Insulin-Like Growth Factor 1 from a Bioengineered Tissue Stimulates Skeletal Muscle Growth in Vitro

Bioengineered tissues transduced to secrete recombinant proteins may serve as a long-term delivery vehicle for therapeutic proteins when implanted in vivo. Insulin-like growth factor 1 (IGF1) is an anabolic growth factor for skeletal muscle that can stimulate myoblast proliferation and myofiber hypertrophy. To determine whether the release of IGF1 from an engineered bioartificial skeletal muscle (BAM) could stimulate the growth of skeletal muscle in a paracrine manner, we established an in vitro perfusion system for genetically engineered IGF1 BAMs. BAMs were bioengineered from C2C12 murine myoblasts stably transduced with a retroviral vector to synthesize and secrete IGF1 (C2–IGF1 BAMs). C2–IGF1 BAMs or nontransduced control C2 BAMs were cocultured with avian BAMS (ABAMs) in constantly perfused biochambers. During 11 days of perfusion, IGF1 levels in the C2–IGF1 BAM perfusion medium increased linearly from 1 to 20 ng/mL. The ABAMs maintained in biochambers with the C2–IGF1 BAMs had significantly more myofibers (69%, p < 0.005) and larger myofiber cross-sectional areas (40%, p < 0.001) compared to those cocultured with control C2 BAMs. These studies show that levels of IGF1 secreted from the C2–IGF1 BAMs are sufficient to produce an anabolic paracrine effect on nongenetically engineered BAMs, and the in vitro perfusion system provides a model for screening proteins effective in stimulating localized skeletal muscle growth.